So apparently DD went to orchestra practice (with the whole orchestra) today and was a little late. She sat down and played with everyone else, and the teacher stopped in horror and tuned the instrument. It was so bad that it had to be tuned again at the group lesson. So maybe that was the main problem. I don't know a lot about string instruments.
If the teacher had to tune it twice in one day, then it is likely either the strings need to be replaced or there is damage to the fine tuners or the pegs. Of course, it is possible that your DD knock it out of tune or the cello experienced a temperature/humidity change during the day. Either way, you should have the rental company check the instrument and repair as necessary.
By the way, it is pretty easy to tune string instruments these days and students are expected to tune their own in class by 6th grade in our district. In the old days, you usually tune against the piano so it can be difficult if you don't have good ears. Nowadays, vibration tuners are popular and cheap or you can use a free app. You basically turn the fine tuners until the visual target lines up. If you are more than a couple of notes off, you may need to adjust the pegs, which can be tricky for a novice (you need to push in while you turn), especially if the pegs are not properly greased and you have a big instrument like the cello or bass.
Anyhow, you should really tune your instrument every time you play, particularly if you can't hear when it is just a little out of tune. Kids do get lazy but I would insist they tune at least once a week.
